ISSUES OF ATOMIC-RESOLUTION STRUCTURE AND CHEMICAL-ANALYSIS BY SCANNING PROBE MICROSCOPY AND SPECTROSCOPY

The ultimate goal of high-resolution microscopy, i.e., the determinati on of structure and chemistry on the atomic scale, has not been achiev ed yet. In the case of scanning tunneling microscopy (STM), the superp osition of atomic and electronic structure information was found to be a critical issue, particularly for semiconductor surfaces. Here, we s how that, in the case of multicomponent systems with large unit cell s ize, the structural analysis is further complicated by the decay behav ior of the surface wave functions, which drastically influences the di stance dependence of STM images. The chemical analysis at the atomic l evel is generally prevented by the inaccessibility of core levels due to the low-energy scale of scanning probe microscopies. However, finge rprints for particular chemical species at the atomic level can be obt ained from tunneling spectroscopy independent of the chosen substrate. Here, we will focus on a particular example of iron adsorbates on dif ferent metal substrates. Finally, the possibility of achieving chemica l contrast on the nanometer scale by friction force microscopy and for ce spectroscopy methods will be discussed. (C) 1996 American Vacuum So ciety.